Conventional vehicle crash discrimination systems typically employ at least one mechanical, electromechanical, or electronic acceleration sensor affixed to the vehicle for sensing vehicle acceleration. The output of the sensors are supplied to a discrimination circuit for comparison to a predetermined threshold value. If the predetermined threshold value is exceeded, the discrimination circuit will output a signal which actuates or deploys a passenger safety restraint, such as an air bag or passive seat belt mechanism.
However, conventional mechanical or electromechanical accelerometer based crash discrimination systems do not account for variations in passenger/occupant conditions in determining whether to actuate the safety restraint. More specifically, conventional accelerometer based crash discrimination systems are generally designed to assume nominal conditions, such as 50th percentile male, actual presence of a vehicle occupant, and failure of an occupant to wear a seat belt. The assumption of these crash conditions are necessary to insure proper actuation of the safety restraint when severe deceleration of the vehicle is detected by the accelerometer. Such assumptions inherently cause unnecessary, undesired, or improperly-timed actuation of the safety restraint in conditions where no occupant is present, in marginal crash situations where a seat belt provides sufficient safety protection for the occupant, or in situations where the occupant is improperly positioned relative to the safety restraint such that actuation of the safety restraint could potentially injure the occupant.
Thus, since conventional crash discrimination systems can not accommodate various occupant conditions which affect the desirability of actuating the safety restraint, they have not proven to be completely satisfactory. In response, the prior art has attempted to overcome these deficiencies by providing arrangements which are generally directed at detecting occupant presence, size, or position relative to some fixed structure in the vehicle. The following are examples of such prior art arrangements.
U.S. Pat. No. 5,413,378 to Steffens, Jr., et al disclose a system for controlling an occupant restraint, such as an air bag, wherein the system utilizes a combination of a set of ultrasonic occupant position sensors, and various seat and occupant weight sensors, to determine occupant weight and position relative to fixed structure with the vehicle.
U.S. Pat. No. 5,398,185 to Omura discloses a system for optimizing deployment of passenger restraint devices which utilizes a combination of a plurality of seat sensors, a card reader for inputting data regarding the physical characteristics of the occupant, and two telecameras to compute a value characteristic of each interior vehicle element and the occupant's estimated behavior relative thereto.
U.S. Pat. No. 5,366,241 to Kithil discloses an overhead-mounted air bag deployment system which utilizes an overhead passenger sensor array to sense position and velocity of an occupant's head so as to control deployment of an air bag, and to detect and provide warning when the occupant is in an unsafe seated condition.
U.S. Pat. No. 5,074,583 to Fujita et al disclose a vehicle collision detection system which utilizes a plurality of seat-mounted sensors to detect occupant seating condition, position, and size in order to optimize inflation of an air bag in a vehicle collision.
In addition, commonly owned U.S. Pat. Nos. 5,446,661 and 5,490,069 each disclose a method and system for vehicle crash discrimination which continuously detects various vehicle occupant positions for optimizing a discrimination analysis to achieve increased efficiency and reliability in actuating a safety restraint.
While these arrangements may have provided an improvement in efficiency over conventional crash discrimination systems, there still exits a need for a crash discrimination system which can further optimize or tailor air bag deployment based on the specific type of occupant present in the vehicle. More specifically, with the increased use and availability of air bags in motor vehicles has come the realization that deployment of an air bag in certain crash situations, and with certain types of occupants, such as infants strapped into a child safety seat, has the potential of causing more harm to the occupant than if the air bag were not deployed.
As noted above, this problem has become particularly acute with infant safety seats. The prior art has attempted to distinguish passengers from infant child seats by using conventional distance measuring techniques to detect the amount and extent of possible occupant movement, or alternatively has used weight sensing arrangements to detect the weight of any object which might be located on the vehicle seat. In either arrangement, threshold values are used to classify an object as either a passenger or an inanimate object.
However, simply using weight sensors or movement monitoring has not provided the level of discrimination between occupant types or the reliability necessary to achieving effective "smart" control over air bag deployment. As a result, a need still exists for a system which can automatically and continually determine occupant type and position in a reliable and cost effective manner.